The present invention relates to a four port electromagnetic coupling device which in the preferred embodiment is a waveguide magic tee. In accordance with the invention, a four port magic tee device is constructed having an E arm of very little or zero length.
Some system applications require the use of a three port device, while others require the use of a four port device. A typical three port device is a waveguide T junction. The three port T junction may be used in some applications such as where the output reflection is low or where there is no requirement for isolation between the two output arms. However, for other applications where, for example, isolation between the output arms is necessary or where the fourth arm is needed as part of the overall microwave circuit, then a four port device such as the waveguide magic tee is used.
A conventional magic tee has four arms which include an E arm, an H arm and two colinear side arms. In the conventional device the E arm, which extends out of the general plane of the other three arms, has a finite length.
For some applications where space requirements necessitate a short height it has been customary to provide a waveguide E bend in association with the E arm, but it has been found that there must be some length to the E arm in order to get acceptable performance. In contrast, in accordance with the invention, a structure has been devised wherein the E arm may be reduced to zero length to thereby make the height of the overall device appreciably smaller than the corresponding height of a conventional magic tee device of comparable performance.
Accordingly, the principal object of the present invention is to provide a magic tee whose E arm can be made to closely approach zero length.